72 AMERICAN HYDEOIDS. 



? GONOTHYRaiA INORNATA Nutting. 



Plate 17, figs. 5-7. 



Gonothyrxa inomala Nutting, Hydroids of the Harriman Alaska Exped., 1901, p. 175. 

 Gonoihyrxa inomala Fraser, West Coast Hydroids, 1911, p. 37. 



Twpliosome} — Colony consisting of a tuft of upright branches springing from a common 

 stem. Height 3.6 cm. The stem proper is very short, almost immediately breaking up into a 

 number of long, delicate upright branches. The branches often themselves brandling in a dicho- 

 tomous manner, sUghtly flexuose and rather thick, although often quite translucent. Imme- 

 diately above each pedicel origin the stem bears usually 2 or 3 strongly marked annulations. The 

 pedicels are alternate, about the length of the hydrothecse, annulated throughout, usually with 

 8 to 12 annulations and decreasing in diameter from basal to proximal ends. They are erect in 

 posture, being nearly parallel with the branch from which they spring. The hydrothecse are 

 subtriangular in outhne, obconical in form, usually about 1 .3 times as long as broad. The margin 

 is even, without regular teeth or ornamentation of any kind. The margin of one hydrotheca is 

 about on a level with the base of the pedicel next above it. 



Gonosome. — Gonangia borne in the axils of the pedicels, rather slender, ovate or obconical 

 ui form, the upper part of the walls sometimes shghtly wrinkled transversely, and with a flat- 

 tened top, upon wliicli, in the older ones, rests a round sack-like "meconidium" or more properly 

 acrocyst without medusoid features, containing developing planulae or sporosacs. In less mature 

 gonangia a single one of these sackUke structures is supported on a blastostyle in the upper part 

 of the gonangium. 



Distribution. — Known only from the type-locality, Yakutat Bay, Alaska. 



There is some doubt regarding the systematic position of this species, but on the whole it 

 appears to be most nearly allied to Gonothyrxa, from which it differs in having no medusoid 

 features to the meconidia. 



Genus OBELIA Peron and Lesueur, modified by Hineks. 



Obelia Peron and Lesueur, Histoire generale des Meduses, Ann. du Mus., vol. 14, 1810, p. 43. 



Campanidaria prolifera Meyen, tJber das Leuchten des Meeree, 1834, p. 198. 



Thaumantias (part) Forbes, British Naked-eyed Medusae, 1848, p. 41. 



Eucope (part) Gegenbauer, Systemes de medusEe, Zeits. Wissensch. Zool., vol. 8, pt. 2, 1857, p. 241. 



Obelia and Eucope L. Agassiz, Cent. Nat. Hist. U. S., vol. 4, 1862, p. 351. 



Obelia and Eucope A. Agassiz, North Amer. Acalephse, 1865, pp. 83, 91. 



Obelia and ScMzocladium Allman, Gymnoblastic Hydroids, 1871, p. 18. 



Obelia and ScMzocladium Browne, Quart. Journ. Micr. Sci., vol. 50, 1906, p. 645. 



Obelia McCrady, Gymnopthalmata of Charleston Harbor, 1857, p. 94. 



Obelia Hincks, British Hydroid Zoophytes, 1868, p. 146. 



Laomedea (part) Broch, Die Hydroiden der arktischen Meere, 1909, p. 189. 



With the exception above noted aU writers since McCrady (1857) that I have consulted 

 have used the name Obelia in its modern sense. While McCrady was the first wi'iter to identify 

 the hydroid form of this genus with the medusa described by Peron and Lesueur, Hiacks in his 

 British Hydroid Zoophytes (1868) was the first one to cast the definition in modern form. 



The foUowing definition wiU serve for the present work. 



Trophosome. — Colony branched; hydrothecse companulate, with a distinct diaphragm. 

 Hydranths with a trumpet-shaped proboscis. 



Gonosome. — Gonangia borne on stems and branches and producing medusse with a disk- 

 hke form, short four-lipped proboscis, 8 lithocysts and usually 8 or more marginal tentacles at 

 hberation. 



KEY TO AMERICAN SPECIES OF THE GENUS OBELIA. 



Main stem fascicled. 



Marginal teeth bicuspidate bicuspidala. 



Marginal teeth not bicuspidate. 



Pedicels not less than one-third length of hydrothecse fragilis. 



Pedicels more than one-third length of hydrothecse plicata. 



' Description of a specimen from the type-locaUty, Yakutat Bay, Alaska, collected by the Harriman Expedition. 



